Re: [Qemu-devel] Better floppy disk support

[Fabrice Bellard <fabrice@bellard.org>]

Mark Jonckheere wrote:
> I propose some patches for better floppy disk support:
> 
> 1. To make "tomsrtbt-2.0.103.ElTorito.288.img" bootable.
> 
> The first one is in fdc.c. It removes the test in fd_init(), since it
> always forces the disk type to 1.44 MB, It is better to give the first
> call to fd_revalidate() a chance to decide if it is a 1.44 or 2.88 drive.

This is incorrect as the BIOS configuration will be invalid. I think it 
is better to probe the disk image size in fd_init (just to select 
between 1.44 and 2.88 drives).

> 2. To make my standalone chntpw-disk bootable (google for bd000607.zip).
> 
> Booting from bd000607.img gives a segmentation error. It seems that the
> bootcode on this floppy (syslinux-ldlinux) does a word-length (16-bit)
> INW at address 0x80 which was translated by function default_ioport_readw()
> in a call to default_ioport_readb(NULL, 0x80) and read_page(NULL, 0x81).
> The second function (in dma.c) needs a (dma_cont *) pointer as its first
> parameter and segfaults when it tries to dereference the NULL-pointer.
> 
> To avoid this problem with word-length io-reads to two adjacent io-ports
> from different or undefined devices it is best to translate it into two
> readb calls each with its own opaque value. The function 
> default_ioport_readw()
> is not the most logical place for doing this, it is better to do this
> upstream in the function cpu_inw().
> 
> I modified cpu_inw() and cpu_outw(), but the same problem could also
> happen with cpu_inl() and cpu_outl().

I have commited a slightly different patch (your patch breaks 16 bit 
I/Os and is too slow).

> 3. To accept "--nics 0" as a legal argument.
> 
> Sometimes it can be usefull to install software without ethernet support.
> I made a minor modification to accept 0 as a legal value for the argument
> --nics. Since the default value remains 1, nothing changes for current 
> usage.

OK.

Fabrice.